Biodegradation of bis(2-chloroethyl) ether by Xanthobacter sp. strain ENV481

Abstract

Degradation of bis(2-chloroethyl) ether (BCEE) was observed to occur in two bacterial strains. Strain ENV481, a Xanthobacter sp. strain, was isolated by enrichment culturing of samples from a Superfund site located in the northeastern United States. The strain was able to grow on BCEE or 2-chloroethylethyl ether as the sole source of carbon and energy. BCEE degradation in strain ENV481 was facilitated by sequential dehalogenation reactions resulting in the formation of 2-(2-chloroethoxy)ethanol and diethylene glycol (DEG), respectively. 2-Hydroxyethoxyacetic acid was detected as a product of DEG catabolism by the strain. Degradation of BCEE by strain ENV481 was independent of oxygen, and the strain was not able to grow on a mixture of benzene, ethylbenzene, toluene, and xylenes, other prevalent contaminants at the site. Another bacterial isolate, Pseudonocardia sp. strain ENV478 (S. Vainberg et al., Appl. Environ. Microbiol. 72:5218-5224, 2006), degraded BCEE after growth on tetrahydrofuran or propane but was not able to grow on BCEE as a sole carbon source. BCEE degradation by strain ENV478 appeared to be facilitated by a monooxygenase-mediated O-dealkylation mechanism, and it resulted in the accumulation of 2-chloroacetic acid that was not readily degraded by the strain.

FIG. 1.

Growth of ENV481 on BCEE (•) or 2-chloroethyl ethyl ether (▪). Symbols represent means (n = 3), and error bars represent 1 standard error.

FIG. 2.

Biodegradation of BCEE (A) and 2CEE (B) by strain ENV481. Symbols represent BCEE (▪), 2CEE (•), DEG (□), and chloride (○). (A) The assays contained 0.18 g (dry weight)/liter (OD₅₅₀ of 0.65) of strain ENV481. (B) The assays contained 0.46 g (dry weight)/liter (OD₅₅₀ of 1.65) of strain ENV481. Symbols represent means (n = 3), and error bars represent 1 standard error.

FIG. 3.

Biodegradation of BCEE by strain ENV481 under anaerobic conditions. Symbols represent BCEE (•), 2CEE (▪), and chloride (▴). Values represent means (n = 3), and error bars represent 1 standard error of the mean. The first sample was collected after 10 min of incubation.

FIG. 4.

Biodegradation of BCEE by strain ENV478. Symbols represent BCEE (•) and 2-chloroacetic acid (▪). Assays contained 1 g (dry weight)/liter ENV478. Values represent means (n = 3), and error bars representing 1 standard error are smaller than the sizes of the symbols.

FIG. 5.

Proposed BCEE biodegradation pathways in strains ENV481 and ENV78. Compounds shown in brackets were not analyzed in this study but are expected based on the other products detected.